#include "stdio.h"
#include "math.h"

int main(){
    float solut(float a,float b,float c,float d);
    float a,b,c,d;
    scanf("%f,%f,%f,%f",&a,&b,&c,&d);
    printf("x=%10.7f\n",solut(a,b,c,d));
    return 0;
}

float solut(float a,float b,float c,float d){
    float x=1,x0,f,f1;
    do{
        x0=x;
        f=((a*x0+b)*x0+c)*x0+d;
        f1=(3*a*x0+2*b)*x0+c;
        x=x0-f/f1;
    } while(fabs(x-x0)>=1e-3);
    return x;
}